Much will depend on the relative position of your plot; is it in a hollow?, at the lowest point of the allotment?; Survey the available drainage on-site. If the allotments are little used, maybe maintenance of ditches etc has been neglected.
Its been a relatively wet winter here in N E Hampshire, where are you?. Your local Environment Agency will put data for groundwater on their website. This will enable you to find the nearest borehole and follow the trends; maybe you can sink a hole in an odd corner and dip the water level to corrolate their findings.
In this area, where I’ve had three seperate plots, the winter level is high, causing difficulties in leaving carrots in the ground-they rot off 3″ down, and PS broccoli died due to roots rotting away.Typically in March, weather becomes more open and things can be planted out.
However, the gradual build -up of raised beds (second year) has reduced issues, the lower paths act as surface drainage ensuring the woodchip covering floats! The underlying London clay retains moisture for almost every season.
If it was easy, then anybody could succeeed!
